Inherited metabolic disorders cause a significant number of brain diseases. A major barrier to treating such diseases is that the inherent nature of the defect results in global distribution of the pathologic lesions within the CNS. This circumstance requires that cells be corrected either throughout the CNS or in key areas where the pathologic consequences are most severe. In this grant we will investigate neural stem cell (NSC)-based approaches to treat the central nervous system (CNS) in neurogenetic disease by delivering a diffusible protein within the brain. The approach is to genetically correct the defect in NSCs in vitro and transplant the corrected cells back into the defective brain. Under the right circumstances, NSCs can migrate within the brain and differentiate into all three major lineages of brain cells. As a test system, we will use a B- glucuronidase (GUSB) deficient mouse, which is a model for human lysosomal storage diseases (LSD). There are >50 individual LSDs and they are responsible for approximately 20% of all inherited childhood genetic diseases that affect the CNS. A common treatment strategy can be used, in principle, for >90% of the LSD's. It is based on the observation that lysosomal enzymes can be secreted from genetically corrected cells, diffuse through tissue, and can be taken up by mutant cells to restore the missing enzymatic activity. Thus, delivery of the modified NSC's to only a fraction of the brain may be able to rescue a large amount of brain tissue. To achieve global delivery of the therapeutic enzyme, the transplanted cells need to be dispersed within the three dimensional space of the brain. We have demonstrated that gene therapy can work in the brains of the GUSB-deficient mice using a clonal cell line. However, there are substantial barriers to achieving permanent and complete correction, particularly in reaching the global lesions in the much larger human brain. We propose to investigate: 1) the transplantation properties and vector gene expression in primary murine NSC's as a model for autologous correction (en vivo gene therapy);2) potential strategies to increase the migration of the NSC's away from the injection site;and 3) the effectiveness of the treatment on the neuropathology and the safety of the transplant recipients. Advances in understanding the transplantation properties of NSC's for treatment in this model should have applicability to the whole class of disease.